Spin on disposable or throw away filters are commonly employed to filter contaminates from fluid systems such as engine and transmission lubrication systems, engine fuel systems, hydraulic systems, and so forth. Such filters generally include a filter element within a deep drawn, relatively thin cylindrical metal housing and a stamped metal cover plate attached to the open end of the housing typically by a rolled lock joint. A central threaded opening is provided in the cover plate for screwing the filter onto a threaded stud of a mounting base. Several openings are provided in the cover plate radially outwardly from the threaded opening for directing fluid through the filter element in the housing An annular gasket on the outside of the cover plate radially outside of the holes in the cover plate serves as an external seal between the filter and the mounting base.
The spin on filters are in essence a pressure vessel subjected to the system pressure One of the problems associated with the currently available spin on filters is that the placement of the seal outside the holes in the cover plate contribute to a large imbalance of forces acting within the filter which results in a rather large force acting on the end of the housing opposite to the cover plate. For example, with an 8 to 12 cm diameter filter at typical system hydraulic pressures, about 1000 kg of force is exerted on the end of the housing. This force is resisted only by the central threaded connection between the cover plate and the mounting base stud. In some applications, the force acting on the end of the housing is sufficient to cause axial elongation of the filter and distortion of the cover plate sufficient to allow leakage past the gasket. In other applications, the rolled lock joint has unfolded.
Various attempts have been made to strengthen the cover plate by making the cover plate from stronger materials, increasing the thickness of the cover plate, and adding reinforcing ribs to the cover plate. Some of those attempts have also included more exotic rolled lock joints. While such modifications to the existing filters have been somewhat effective, the major disadvantage is that all the modifications add to the cost of building the filter with the cost passed on to the customer through higher prices.
The present invention is directed to overcoming one or more of the problems as set forth above